全文获取类型
收费全文 | 1305篇 |
免费 | 146篇 |
国内免费 | 199篇 |
专业分类
测绘学 | 199篇 |
大气科学 | 240篇 |
地球物理 | 273篇 |
地质学 | 336篇 |
海洋学 | 152篇 |
天文学 | 20篇 |
综合类 | 102篇 |
自然地理 | 328篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 42篇 |
2021年 | 53篇 |
2020年 | 55篇 |
2019年 | 63篇 |
2018年 | 56篇 |
2017年 | 60篇 |
2016年 | 44篇 |
2015年 | 60篇 |
2014年 | 80篇 |
2013年 | 110篇 |
2012年 | 79篇 |
2011年 | 64篇 |
2010年 | 49篇 |
2009年 | 84篇 |
2008年 | 54篇 |
2007年 | 77篇 |
2006年 | 84篇 |
2005年 | 72篇 |
2004年 | 73篇 |
2003年 | 38篇 |
2002年 | 45篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
排序方式: 共有1650条查询结果,搜索用时 140 毫秒
131.
浙中一次强对流天气动力热力场和雷达回波特征分析 总被引:2,自引:0,他引:2
利用NCEP再分析资料、常规气象观测和区域自动站观测资料、闪电及多普勒雷达天气资料,对2013年5月29日浙中局地强对流天气过程的环境场、触发机制和雷达回波特征进行了分析。结果表明:局地强对流天气是在东北冷涡背景下产生的;高空冷平流南侵、低层暖平流北上,有利于大气对流不稳定度进一步加大;在热力不稳定能量增长储存条件下,冷空气、地面辐合线与中低层切变线是强对流天气的重要触发机制,地面辐合线对强对流天气还具有组织作用;沿等熵面移动的较大位涡有利于超级单体风暴的发生和发展;初夏0 ℃层高度偏高,但在满足强烈位势不稳定、中等风垂直切变以及低层充足水汽条件下仍可以导致局地小冰雹的产生;地面大风过程是低空暖湿气流入流在快要进入上升气流区时受到上升气流区的抽吸作用而加速导致生成的;多个回波强核被中气旋组织在一起,形成超级单体风暴造成了局地强风雹天气。 相似文献
132.
德州气候变化与建筑物防腐 总被引:2,自引:0,他引:2
利用德州11县市1951~2005年温度、降水资料,计算气候干燥度,1981~2005年与1951~1980年相比全市干燥度由1.45增大到1.64,已由原来的半湿润气候变化为半干旱气候。各县市降水量呈减少趋势,平均每10年减少19.64mm;气温呈上升趋势,平均每10年升高0.11℃,冬季升高0.30℃,冬季增温显著,北部县市已由原来的冰冻区变化为微冻区,全市均为微冻区。由于气候条件变化,相应场地环境类别与腐蚀介质指标的调整系数标准应作调整改变,场地环境类别由Ⅱ类转变为Ⅰ类,腐蚀介质指标的调整系数均取0.9。 相似文献
133.
Yu. F. Yurovsky 《Bulletin of the Crimean Astrophysical Observatory》2007,103(1):30-38
The eclipse observations were performed at the Laboratory of Radio Astronomy of the CrAO in Katsiveli with stationary instrumentation of the Solar Patrol at wavelengths of 10.5 and 12.0 cm. The data obtained were used to determine the brightness temperature of the undisturbed Sun at solar activity minimum between 11-year cycles 23 and 24: T d10.5 = (43.7 ± 0.5) × 103 K at 10.5 cm and T d12.0 = (51.8 ± 0.5) × 103 K at 12.0 cm. The radio brightness distribution above the limb group of sunspots NOAA 0866 was calculated. It shows that at both wavelengths the source consisted of a compact bright nucleus about 50 × 103 km in size with temperatures T b10.5 = 0.94 × 106 K and T b12.0 = 2.15 × 106 K located, respectively, at heights h 10.5 = 33.5 × 103 km and h 12.0 = 43.3 × 103 km above the sunspot and an extended halo with a temperature T b = (230–300) × 103 K stretching to a height of 157 × 103 km above the photosphere. The revealed spatial structure of the local source is consistent with the universally accepted assumption that the radiation from the bright part of the source is generated by electrons in the sunspot magnetic fields at the second-third cyclotron frequency harmonics and that the halo is the bremsstrahlung of thermal electrons in the coronal condensation forming an active region. According to the eclipse results, the electron density near the upper boundary of the condensation was N e ≈ 2.3 × 108 cm?3, while the optical depth was τ ≈ 0.1 at an electron temperature T e ≈ 106 K. Thus, the observations of the March 29, 2006 eclipse have allowed the height of the coronal condensation at solar activity minimum to be experimentally determined and the physical parameters of the plasma near its upper boundary to be estimated. 相似文献
134.
随着建设活动的日益频繁以及建筑范围的扩大,局部表层岩溶被揭露,出现不同于基坑整体失稳的局部岩溶充填物的失稳现象,此失稳现象往往和地下岩溶水相联系,因为处于局部,不能引起设计人员的重视,在沟槽中岩溶水动力的作用下失稳,可能产生较大的工程问题。 相似文献
135.
136.
137.
Given the advances in satellite altimetry and multibeam bathymetry, benthic terrain classification based on digital bathymetric models (DBMs) has been widely used for the mapping of benthic topographies. For instance, cobalt-rich crusts (CRCs) are important mineral resources found on seamounts and guyots in the western Pacific Ocean. Thick, plate-like CRCs are known to form on the summit and slopes of seamounts at the 1 000–3 000 m depth, while the relationship between seamount topography and spatial distribution of CRCs remains unclear. The benthic terrain classification of seamounts can solve this problem, thereby, facilitating the rapid exploration of seamount CRCs. Our study used an EM122 multibeam echosounder to retrieve high-resolution bathymetry data in the CRCs contract license area of China, i.e., the Jiaxie Guyots in 2015 and 2016. Based on the DBM construted by bathymetirc data, broad- and fine-scale bathymetric position indices were utilized for quantitative classification of the terrain units of the Jiaxie Guyots on multiple scales. The classification revealed four first-order terrain units (e.g., flat, crest, slope, and depression) and eleven second-order terrain units (e.g., local crests, depressions on crests, gentle slopes, crests on slopes, and local depressions, etc.). Furthermore, the classification of the terrain and geological analysis indicated that the Weijia Guyot has a large flat summit, with local crests at the southern summit, whereas most of the guyot flanks were covered by gentle slopes. “Radial” mountain ridges have developed on the eastern side, while large-scale gravitational landslides have developed on the western and southern flanks. Additionally, landslide masses can be observed at the bottom of these slopes. The coverage of local crests on the seamount is ~1 000 km2, and the local crests on the peak and flanks of the guyots may be the areas where thick and continuous plate-like CRCs are likely to occur. 相似文献
138.
Increasing recognition of the value of practice-based or experiential knowledge in natural resource management justifies the creation of a new category of articles in Society & Natural Resources that we are calling Practice-Based Knowledge (PBK). The rationale for focusing on PBK is due to its key role in the emergence of hybrid governance institutions across state, market, and civil society, understanding the complexity of dynamic socioecological systems, recognizing the challenges of multiple knowledge systems and context-specific practices, embracing the power of informal institutions and civic science, and engaging debates on the growing prevalence of market-oriented conservation. The goal is to provide a dedicated space within the published, peer-reviewed literature for scholars, government officials, nonprofit managers, and engaged citizens to share experiences informed by practical action. Relevant and timely practice-based insights may improve understanding and management of social and ecological processes and systems, while also offering the potential to contribute to theory. 相似文献
139.
Traditional ecological knowledge (TEK) guides resource management across the globe, but is at risk amid social and ecological change. This has prompted numerous calls for TEK maintenance efforts, but these remain largely unexamined in the literature. Here, we discuss three examples of in situ TEK maintenance from Malekula Island in Vanuatu, locally known as kastom schools. Based on qualitative data, we find that the kastom schools may create several opportunities to maintain TEK (e.g., establishing local control over education), and argue that they represent the creative and adaptive management of tradition in dynamic social–ecological contexts. However, a number of challenges, both practical (e.g., lack of funding) and epistemological (e.g., changing modes of cultural transmission), threaten the efficacy of the kastom schools. We argue that in situ modes of TEK maintenance have promise, but that issues of power and heterogeneity require serious consideration if such measures are to succeed. 相似文献
140.
教学科研的深度融合是研究型大学的共同特点,但各个大学实现融合的模式仍存在差异。本文拟基于地方文化传统和周边产业发展需求,探索地方对大学主导功能的影响,并结合对英美典型研究性大学的案例剖析,研究不同大学教学科研融合发展的主要立足点不同的内在原因。研究显示,地方不仅为大学的发展提供资金和基础设施等方面的支持,也需要大学提供人力资本、知识创新等方面的服务,因此,大学的主导功能与地方文化经济环境密切相关,而教学科研的融合则往往立足于大学的主要功能。例如,牛津大学以人才培养为重点就深受英国传统文化的影响,哈佛在基础研究方面的卓越贡献也与其追求真理的文化传统有关,而斯坦福大学以服务产业发展促进人才培养与科研紧密融合的模式也受到实用教育理念的影响。总的看来,研究型大学都应该力促教学科研的深度融合,这是其承载文化传播和知识创造功能的基础,但就具体大学而言,很有必要适应特定地方的文化环境,探索适合的教学科研融合发展模式,而不要陷入盲目模仿的误区。 相似文献